Ionic discharge device



May 24, 1949. c. DEPEW 2,471,263

IONIC DISCHARGE DEVICE Filed May 24, 1946 2 Sheets-Sheet 1 FIG. 4 44 v26 Ii I ll 46 PM w 20 W 20 I 7 I l h/ 24 24 a2 40 as "K a HI 1 INVENTORy C. DEPE W AT TOR/V5 V May 24, 1949. c. DEPEW 2,471,263

IONIC DISCHARGE DEVICE Filed May 24, 1946 2 Sheets-Sheet 2 FIG. 9

FIG. 6

1. 2 5 7? r Q i FIG. 7 f" :31. ll 23 INVENTOR c. DEPEW A TTORNE YPatented May 24, 1949 UNITED STATES PATENT OFFICE IONIC DISCHARGE DEVICECharles Depew, Oakland, N. J., assignor to Bell Telephone Laboratories,Incorporated, New

York, N. Y., a corporation of New Yorl Application May 24, 1946, SerialNo. 672,010

12 Claims. 1

This invention relates to ionic discharge devices and more particularlyto high frequency spark gap devices especially suitable for use as pulsegenerators and capable of handling a high power output.

'In high voltage pulse signaling systems employing spark gap dischargedevices for generating high frequency pulses of high periodicity, theintense heat generated in the gaps of the individual devices, due toionization and breakdown at the high rate of discharge, causessputtering of the electrodes, and particularly the cathode, whicheventually shortens the efiicient operating life of the devices becauseof alteration in the critical spacing of the gap between the electrodes.

While sputtering may be minimized by suitable choice of electrodematerials, electrode spacing and configuration, gas mixture and pressureand theoperating range of the device, a primary fault of priorconstructions of the coaxial electrode type is the lack of stablesymmetrical relation between the electrodes. Since the discharge occursover a path of minimum resistance, it is readily seen that eccentricitybetween coaxial electrodes will produce a preferential path for thedischarge at the minimum distance between the electrodes. Consequently,sputtering of the cathode material will be enhanced by displacement ofthe cathode with respect to the anode of the device. Furthermore, thesurrounding cathode, which has the greater mass andsurface area of theelectrodes in the device, is readily displaced if only supported by aslender conductor sealed through one end of the enclosing vessel. Thesedisadvantages are accentuated when the spark gap discharge devices aresubjected to severe usage as a result of shock or vibration such asoccurs due to percussion on board naval vessels or in airplanes whenlanding.

One object of this invention is to insure axial symmetry between theelectrodes in spark gap or other conduction discharge devices.

Another object of the invention is to facilitate the fabrication of thedevice whereby accurate space relation between the electrodes isattained.

A further object of the invention is to overcome shock and vibrationconditions which deleteriously affect the static and dynamiccharacteristics of the device.

Another object of the invention is to prolong the operating life of suchdevices with high elliciency and increase the power dissipation ratingthereof at high output,

Another object of the invention is to simplify the manufacturingprocedure of the device.

Another object of the invention is to improve the rigidity of theelectrode assembly in the device so that eccentric space relationbetween the electrodes is substantially eliminated.

These objects are attained in accordance with features of this inventionby an assembly of electrodes in the enclosing vessel involving acylindrical metallic cathode and an axial solid anode which arecoaxially mounted on cup-shaped terminal members hermetically sealed toopposite end portions of the enclosing vessel. This constructioneliminates extraneous cemented terminals for the device, facilitates thefabrication and mounting of the electrodes, insures stability in spacerelation between the electrodes and enhances the operating life of thedevice by insuring freedom from preferential discharge between theelectrodes.

A beneficial feature attending the assembly of the device of thisinvention relates to the accuracy in critical space relation of theelectrodes attained in the fabrication of the device. This desideratumis realized by mounting the separate electrodes on cup-shaped metallicmembers which are sealedto opposite ends of a hollow cylindricalvitreous vessel in such a manner that accurate concentricity of thecathode and vessel is produced in sealing.

Another feature of the invention relates to the mounting of thecylindrical cathode on its terminal member to insure high rigidity andfixed relation thereof to the anode in the device. This constructioninvolves the provision of an annular flange on the internal surface ofthe cathode terminal member and rigid-1y securing the cylindricalcathode thereto in'concentric relation to the peripheral sealing rim ofthe terminal memher.

A further feature of the cathode assembly relates to the formation ofthe cathode terminal member to facilitate the gauging of the anodemounting in the vessel, The cathode terminal member is provided with acoaxial tubular extending portion having the same diameter as thecathode and, after the cathode assembly is sealed to the enclosingvessel, the tubular portion and cathode both cooperate in accuratelycentering the anode assembly on the opposite end of the vessel. Thetubular portion is terminated by an inverted cup closure which seals thecathode terminal member and forms a contact portion for the cathode.

Another feature of the invention relates to the anode construction whichfacilitates pumping, filling and sealing the vessel in the completion ofthe device. This construction includes the mounting of an anode standardconcentrically on a perforated platform within the anode terminal memberand providing a metallic tubulation at the center of the terminal memberwhich is sealed off after processing the device. The tubulation isenclosed in an extension of the terminal memher which is capped with aprotective closure and serves as a contact for connecting the device inan operating circuit.

A further feature of the invention relates to the assembly of twodevices in series relation for multiple-gap operation in which the anodecontact of one device is in telescopic relation with the cathodeterminal of another device. This construction includes a circularcompression resilient member which engages both the anode contact andthe cathode cavity terminal portions of the respective devices whenmounted in telescopic relation to insure positive continuity between thedevices when connected in series relation.

These and other features and advantages of the invention will be moreclearly understood from the following detailed description whenconsidered with the accompanying drawings which show illustrativeembodiments of the invention.

Fig. 1 is a perspective view of the complete assembly of a dischargedevice illustrative of this invention with a portion of the vesselbroken away to show the disposition of the electrodes;

Fig. 2 shows in elevation a sectional view of the device of Fig. 1 toillustrate the symmetrical relation of the spark gap electrodes in thevessel;

Fig. 3 is a cross-sectional view of the coaxial electrodes in the vesseltaken on line 3-3 of Fig. 2;

Figs. 4 and 5 are cross-sectional views illustrating successive steps inthe sealing of the electrode assemblies to opposite ends of the vesselto insure accurate concentricity of the electrodes in the device;

Fig. 6 is a perspective exploded view showing the various componentassemblies entering into the fabrication of the device illustrative ofthis invention;

Fig. '7 is an enlarged cross-sectional view of a portion of the anodeassembly of the device illustrating the detailed construction of theseal and the protective closure therefor;

Fig. 8 illustrates an improved mounting assembly of a two-gapcombination involving devices of this invention in series relation;

Fig. 9 is an enlarged view of the resilient coupling for the seriescombination of devices, taken on the line 99 of Fig. 8, and illustratingthe large surface contact provided by the coupling between the devices;and

Fig. 10 is an enlarged perspective view of the ring contact, shown inFig. 9, having bent resilient fingers on opposite sides of the ring toprovide positive contact with the respective walls of the terminals ofthe series connected devices.

The discharge device of this invention, in one aspect, is represented asa high voltage-high frequency spark gap pulse generator device capableof supplying a large output of the order of 300 amperes peak current,the construction being suificiently rugged to withstand severe handlingand working conditions without altering the critical gap spacing betweenthe electrodes. These electrodes are subjected to intense ionicdischarges at high voltages of the order of 3 to 10 kilovolts andoperate in a pulse frequency range of 1,000 to 1,600 pulses per secondwith a pulse period of 5 10- per second. Under these high operatingconditions and the intense sparking energy dissipated in the device, tominimize sputtering of the electrodes, it is essential to attainabsolute concentricity between the electrodes and maintain such accuracyof space relation throughout the operating life of the device regardlessof the severe handling and usage of the device in operational equipment.

In order to attain the high power rating developed by the deviceillustrative of this invention, the surface area of the cathode isincreased to dissipate the heat energy generated in the ionizingatmosphere or the device. The mass of the cathode and its mounting,therefore, must not endanger the critical spacing between the electrodesto insure efficient operation at high pulse periodicity over a longlife. If shocks or vibrations are permitted to endanger theconcentricity of the electrodes or if the electrodes are initiallyeccentric with respect to each other, it is readily seen thatpreferential or spot discharges will 00- our in the gap between theelectrodes at the' point of minimum distance between the electrodes andresult in short life, due to erosion or sputtering effects of the spotdischarges. Such effects alter the space relation of the electrodes withconsequent unstable characteristics and degenerative effects uponoperation of the device.

The attainment of stability in operating characteristics and asufiiciently rugged construction to withstand severe usage is realizedby an assembly as shown in the drawings.

Referring particularly to Figs. 1 to 3, inclusive, the high voltagespark gap device embodies as main components, a vitreous enclosingvessel 20 open at opposite ends, a pair of metallic cap terminal members2! and 22 closing the ends of the vessel, a rod anode support 23centrally located in the vessel and supported by the terminal cap 2i anda cylindrical cathode 2G coaxially surrounding the anode and mounted onthe cap 22 of the vessel.

The cap terminal members or closures 2i and 22 are preferably formed ofa nickel-iron-cobalt alloy having a thermal coefficient of expansivityat 500 C. of 5.71 to 621x10 per degree centigrade, to match the averagethermal expansion coefficient of the vitreous bulb or vessel 26, whichis formed of a hard bore-silicate glass, such as 7052 glass,commercially obtainable from Corning Glass Company. The cap members arefused. into the open ends of the vessel to form hermetically sealedjoints therewith which will withstand the temperature ranges ofoperation or the device without undue strains at the sealed joints andto maintain a stable ionic discharge in the gaseous filling within thevessel. This filling may be composed of a mixture of 75 per centhydrogen and 25 per cent argon at a pressure of 60 to '70 centimeters ofmercury.

Since the discharge is initiated by break-down of the gap betweeninactive cold electrodes across the ionizing path in the gas mixture, toachieve conduction between the concentric electrodes whereby highcurrent pulse generation is realized, it is desirable to overcome theinherent dielectric resistance in the gap between the electrodes byintroducing a free electron ionizing medium in the discharge space toeffect conduction at a lower voltage than would be possible without themedium. This sustaining substance, specifically radium bromide, isapplied to the inner surface of the cathode in the form of painted spots25, to provide initial free electrons in the gap to facilitateionization and breakdown of the discharge gap on starting. The radiumbromide is decomposed on heating during the final processing of thedevice after assembly to provide elemental radium in the gap so that thepresence of free electrons is assured. The starting discharge voltagemay be of the order of 6 kilovolts, but after initial break-down theoperating voltage may be reduced to 4.5 kilovolts, with the pulsefrequency attained by a trigger voltage of 8 kilovolts.

The high voltage operation, high current output and high periodicity ofpulse generation capable of being attained in the device imposestringent requirements on operation of the device. For example, coronadischarge must be minimized in order to prevent premature arcing orprefiring of the discharge before the minimum trigger voltage isimpressed 0n the electrodes. Another difficulty engendered in the highvoltage operation of the device is sputtering or diffusion of electrodematerial in the discharge and particularly the cathode or negativeelectrode which is subjected to the intense spark discharge in the gap.These effects are substantially eliminated or materially inhibited bythe construction of the device whereby stable operation is insured and arelatively long useful life is attained. Furthermore, the critical spacerelation of the electrodesin the discharge gap is maintained constantsubstantially throughout the life of the device due to the rigidmounting of the electrodes and the absolute con'centricity of theelectrode spacings so that preferential discharge to a concentrated spotor area of the cathode is eliminated and thereby alteration of the gapspacing is avoided. Also, the device can withstand rough handling andusage without the gap spacing being endangered by shocks or vibrationseven on board naval vessels or other carriers subjected to intensepercussions.

The configuration of the electrodes, their mounting and fabrication inthe enclosing vessel 20 and the constant space relation, whereby theabove results are attained in accordance with features of thisinvention, will now be described with reference to the drawings. Theenclosing Vessel 20 is provided with a small diameter neck portion 26which is made comparable to the diameter of the cap closure 2! so thatthe periphery of the latter can be hermetically sealed to and embeddedin the boundary of the glass to form a hermetically sealed union andrigidly anchor the closure to one end of the vessel to serve as theterminal member of the anode. The closure member 2| is provided with acentral, outwardly extending metallic tubulation 21 which is surroundedby a metallic flanged sleeve 28 in concentric relation to the tubulation21. A truncated conical metallic platform 29 having a flanged base 3% isconcentrically secured within the closure 2| and is provided with aplurality of circular apertures 3! around the surface, to form communicating passageways from the interior of the vessel 20 to the exhausttubulation 27. The anode supporting rod 23 extends centrally from theplatform 29 and a cylindrical anode plug 32 having a rounded nose issecured to the rod 23 by brazing a ring of high melting point metal 33,such "as copper, in a notch formed on the plug at the juncture with therod. The anode plug 32 is preferably formed of nickel and supported onthe standard or rod 23. The latter preferably is formed of steel, thestandard being spotwelded to the platform 29 by ring-welding the buttontermination 34 on the inner surface of the platform with the standardprojecting through a central aperture in the platform. Since the sleeve-23 and platform 29 have a large surface contact with opposite sides ofthe closure member 2 l it is preferable to form these members of anickeliron-cobalt alloy, to avoid expansion strains on the glass seal ofthe neck portion of the vessel.

The tubulation 21 permits the device to be evacuated in the finalprocessing of the assembly and provides means for introducing thedesired gas mixture of hydrogen and argon at the predetermined pressurefor efficient operation of the device. The tubulation is then sealed offby pinch-welding and a metallic cap 35 is welded over the sleeve 28 toform a protective covering for the tubulation 21 and provide acylindrical contact for the anode terminal closure of the device. Thisdetailed assembly of the anode construction is shown in Fig. 1.

The opposite end of the enclosing vessel 29 is provided with a largediameter skirt portion 36 which is only slightly smaller than thediameter of the main body portion of the vessel. The cap closure 22 hasa diameter comparable to the skirt portion 36 of the vessel so that itsperipheral flange may be hermetically sealed to and embedded in the rimportion of the skirt 36 of the vessel, to provide a large surfaceterminal and metallic closure for the device. The closure is providedwith an outwardly extending integral sleeve portion 31 concentric withrespect to the flanged seal portion of the cap member. A flanged ring38, preferably of a nickel-iron-cobalt alloy, is concentricallyring-welded to the inner surface of the closure member 22 and has adiameter slightly larger than the sleeve portion 31 of the closuremember, the ring forming a rugged base support for the cylindricalcathode 24. The cathode 24 is preferably formed of aluminum, since thismetal has a low diffusion rate in the type of discharge encountered inthe operation of the device. The cathode is formed, e. g. machined tohave a main cylindrical body portion of sufficient length tosubstantially enclose the anode plug 32, and a cylindrical skirt portion39, of larger diameter; to surround the termination of'the plug and aportion of the standard 23 supporting the plug, to provide a shieldbeyond the main discharge area between the electrodes and therebyprevent the extension of the discharge into the surrounding area withconsequent blackening of the wall of the glass vessel 20.

The main inner surface of the cylindrical cathode is polished, toprovide a high gloss surface, thereby eliminating any burrs or pointswhich might serve as corona points to cause unstable operation in thedischarge between the electrodes. The cylindrical cathode is alsoprovided with a thin wall portion adjacent the support ring 38 so thatthis portion has the same diameter as the external diameter of the ring38 and the thin portion is rigidly attached to the ring 38 by nickelironalloy rivets 40, to insure a substantial mounting of the large masscathode on the closure member 22. In this arrangement, the internaldiameter of the cathode is the same as the diameter of the sleeveextension 3'1 of the closure member 22. The large sleeve opening in theclosure 22 is terminated by a recessed metallic cap 4!, preferably ofnickel-plated copper, which is mounted in reentrant relation to thesleeve portion 3? and provided with a curved lip 42 which is sealed witha lower melting point solder, such as silver copper alloy 43. Therecessed cap 4| forms a socket terminal for connecting the cathode to anex-' ternal circuit. It will be noted that the terminal contacts of therespective electrodes in the device have difierent configurations anddimensions and are coaxially mounted on opposite ends of the enclosingvessel so that the device can be inserted readily in an operatingcircuit without error since the terminal configurations of theelectrodes are self-indexing and proper connection of the electrodes totheir respective voltage sources is assured.

Prior to the assembly of the closure cap members on the ends of theenclosing vessel, the electrodes are individually mounted concentricallyon the respective closure members while employing the turned peripheralportion of the cap member as an index for the mounting of the respectiveelectrodes accurately in concentric position with respect thereto. Afterthis operation is completed, the cathode assembly is sealed to thelarger diameter end 36 of the enclosing vessel 20, as, shown in Fig. 4.A cylindrical jig or gauge 44 is inserted in the small neck portion 26of the enclosing vessel 20 and the cathode assembly is introducedthrough the larger diameter end of the vessel 28 so that the gauge fitswithin the internal diameter of the cathode 24. In this position, theglass skirt portion 36 of the enclosing vessel is heated to render theglass plastic and also to heat the flange portion of the closure member22 so that the periphery of the cup is embedded in the plastic glass toform a vacuum-tight sealed joint. After this operation is completed andthe seal has cooled sufiiciently to remove strains, the gauge 44 may beremoved. The cathode 24 is accurately centered with respect to the axisand cylindrical wall of the enclosing vessel 20 so that it will alwaysmaintain this position in the vessel since the cap member 22 issufficiently rigid to prevent flexing movement thereof which would alterthe relationship of the cathode with respect to the cylindrical surfaceof the vessel.

The mounting of the anode assembly on the opposite end of the enclosingvessel is shown in 5, in which another cylindrical gauge 45 is insertedthrough the sleeve portion 31 of the closure member 22 and the innersurface of the cathode 24. Prior to this operation, the cap closure l!is not assembled on the sleeve portion 3? of the closure 22 so that thissleeve portion is open and since it has the same diameter as the cathodethe gauge 45 will accurately slide into the assembly. The cylindricalgauge 45 is provided with an accurately shaped socket 46 to receive theanode plug 32 which was previously assembled on the terminal member 2|and mounted in position through the neck portion 26 of the enclosingvessel, as shown in Fig. 5. The neck portion is then heated to renderthe glass plastic and when the proper sealing condition is attained aslight longitudinal movement of the gauge 45 will permit the rim of theclosure cap member 2! to be embedded in the neck portion 26 of thevessel, to provide a hermetic seal joint and insure absoluteconcentricity of the anode with respect to the cylindrical inner wallsurface of the cathode. After the gauge 45 is removed, the closure cap4! is sealed to the sleeve 3'! as previously described. The mounting ofthe large area cylindrical cathode on the short annular support 38within the cup-shaped terminal memher 722 ri idly maintains the cathodein concentric relation to the anode plug 32. The latter is rigidlysupported on the standard attached to the cup-shaped terminal member 2]on the oppoill;

site end of the vessel so that constant symmetry is maintained in thedischarge gap between the electrodes.

Another feature of the construction of the device in accordance withthis invention relates to the mounting of two or more discharge devicesin series relation for multi-gap operation, as shown in Fig. 8. The twodevices are mounted in series relation on a mounting plate 41 havingtwin pairs of trianguar-shaped walls 48 bent upwardly at right angles toform mounting cradles for the devices. The devices are clamped insemi-circular clamp members 49 attached to the side walls 48 of themounting with the anode ter-. minal 35 of one device in telescopicrelation with the cathode terminal contact ll of the preceding device.The telescopic union is achieved by a resilient annular compressionmember, shown more clearly in Figs. 9 and 10. The compression springmember is a metallic ring Bil, preferably of beryl liurn copper. It isformed of a central strip member having a plurality of equally spacedfingers projecting outwardly on opposite sides of the the fingers 5! onone side being bent outwardly and downwardly and the fingers 52 on theopposite side being bent inwardly and upwardly to engage the socketclosure cup 4| and the cylindrical terminal 35, respectively, of thecontacts of the respective devices in telescopic relation.

A strap terminal member 53 may be welded to the annular contact 50 toprovide a medial terminal for applying the trigger voltage to the seriescombination, while the negative side of the high voltage system isconnected to the socket 4! of one device and the positive side of thevoltage source is connected to the cap terminal 35 of the other device.

While the invention has been disclosed with respect to a particularembodiment of a spark gap discharge device, it is of course understoodthat various modifications may be made in the assembly which wouldreadily adapt the invention to various other devices of like nature,such as high vacuum condensers, high vacuum switches, mercury vaporrectifiers, trigger control devices and other electronic dischargedevices, without departing from the scope of the invention as defined inthe appended claims.

What is claimed is:

1. An ionic discharge device comprising a vitreous enclosing vesselhaving open ends of different diameters, a metallic cap member sealed toand closing the smaller end of said vessel, a solid anode supported bysaid member and extending xially within said vessel, an aperturedmetallic cap member having a central tubular extension sealed to andpartially closing the larger diameter end of said vessel, a cylindricalmetallic cathode rigidly affixed to said apertured cap member andcoaxially surrounding said anode within said vessel, the inner diameterof a portion of said cathode being of the same dimension as the innerdiameter of the tubular extension of said apertured cap member, and aninverted recessed closure fitted into said tubular extension.

2. ionic discharge device comprising a vesso]. open at opposite ends, ananode and a cathode positioned within said vessel, metallic closuremembers sealed to opposite ends of said vessel,- a metallic perforatedplatform concentrically secured to one of said closure members, acentral post proiecting inwardly from said platform, said anode beingattached to said post, and a flanged ring concentrically aflixed to theother of said closure members within said vessel, said cathode.

being carried by said ring and coaxially spaced from said anode.

3. An ionic spark gap discharge device comprising a vessel open atopposite ends, metallic closures sealed to the ends of said vessel, ametallic perforated platform secured to one of said closure members, acentral post projecting inwardly from said platform, a solid anodeattached to said post, a flanged ring concentrically affixed to saidother closure member within said vessel, a cylindrical metallic cathoderigidly mounted on said ring and surrounding said anode, and a recessedcap member in the central portion of said other closure member.

4. An ultra-high frequency spark gap device for high power outputoperation, comprising coaxially mounted cathode and anode electrodes, acylindrical vitreous vessel enclosing said electrodes, metallic terminalcap members sealed to opposite ends of said vessel and supporting saidelectrodes therein, one of said members having a smaller diameter thanthe other, a sleeve on said smaller diameter member, a coaxial exhausttube within said sleeve, and a cap carried by said sleeve and protectingsaid exhaust tube.

5. An ultra-high frequency spark gap device for high power outputoperation, comprising axially mounted cathode and anode electrodes, acylindrical vitreous vessel enclosing said electrodes, metallic terminalcap members sealed to opposite ends of said vessel and supporting saidelectrodes therein, one of said members having a larger diameter thanthe other, coaxial sleeve portions extending from opposite sides of saidlarger diameter member, said cathode being attached to the inner sleeveportion on said member, and a recessed cap fitted in the outer sleeveportion.

6. An ultra-high frequency spark gap device for high power outputoperation, comprising 00- axially mounted cathode and anode electrodes,a cylindrical vitreous vessel enclosing said electrodes, metallicterminal cap members sealed to Opposite ends of said vessel andsupporting said electrodes therein, one of said members having a largerdiameter than the other, coaxial sleeve portions extending from oppositesides of said larger diameter member, said cathode being attached to theinner sleeve portion on said member, said cathode and outer sleeveportion having the same internal diameter, and a recessed cap fitted inthe outer sleeve portion.

7. A high voltage spark gap comprising a vitreous receptacle ofcylindrical form having a neck portion at one end, a metallic closuresealed to said neck portion, an apertured platform member afixed to saidclosure, a central tubulation in said closure communicating with thespace in said receptacle through said member, a central standardsupported by said platform member, an anode plug projecting from theinner end of said standard, a flanged metallic ring closure sealed tothe opposite end of said receptacle, an internal annular member securedto said ring closure, a cylindrical cathode surrounding said anode andrigidly afiixed to said annular member, and a reentrant metallic capsealed to and closing said ring closure.

8. A mounting comprising a plurality of high frequency spark gap devicesarranged in series relation, said devices each having metalliccylindrical and circularly recessed terminal portions at opposite endsthereof, the cylindrical terminal portion of one device being intelescopic relation to the recessed terminal portion of another device,and an annular compression spring member interposed between saidterminal portions in telescopic relation.

9. A twin-gap pulse device mounting comprising a pair of spark gapdevices in series relation, one of said devices having a protrudinganode terminal telescopically fitted into a recessed cathode terminal ofthe other device, and a resilient member of circular configurationhaving reversely bent inner and outer fingers engaging the coaxialsurfaces of said terminals in telescopic relation.

10. In a spark gap discharge device, an electrode assembly comprising ametallic closure cap sealed to one end of an insulating enclosingvessel. an apertured platform spaced from and supported within saidclosure cap, a standard rigidly fixed to said platform, and an electrodesecured to the free end of said standard.

11. In a spark gap discharge device, an anode assembly comprising ametallic closure cap sealed to one end of an enclosing vessel, afrusto-conical metallic member centrally mounted Within the confines ofsaid closure cap, said member having distributed openings adjacent theperiphery thereof, and a rod anode centrally affixed to said member.

12. In a spark gap discharge device, an anode assembly comprising anapertured metallic closure cap sealed to one end of a vitreous enclosingvessel, a metallic platform mounted within said cap in concentricrelation to the periphery thereof, a projecting tubulation centrallysealed to said cap, an anode supported on said platform, a sleeve onsaid cap surrounding said tubulation, and a protective cover memberclosing said sleeve over said tubulation.

CHARLES DEPEW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,397,982 Salzberg Apr. 9, 19462,411,184 Beggs Nov. 19, 1946 2,411,241 Arnott et al Nov. 19, 19462,422,324 Watrous June 17, 1947

